The bird straps have come from a number of places. I have made some from cow leather, deer hide, and most recently paracord. I've had a few made and given to me by people that know I'm into such things. I have also made some and given them away. In my opinion deer hide or another thin, soft hide is the best leather because it cinches down much tighter than full grain cow leather. The same is true of paracord, it just doesn't look traditional. What it lacks in form it makes up for in function. Only one of my straps was purchased. I got it from Dunn's about twenty-five years ago.
This is my latest creation. I made it last year and call it "The Weekender". The double snaps allow it to be taken apart and a single strap carried on a belt loop or cartridge bag for a day of shooting. It will hold birds for two people for two days.